Merge pull request #10310 from signify-nz/fix/10308--datacolumns-in-csv-export

FIX Use DataColumns content when available in CSV export

src/Forms/GridField/GridFieldExportButton.php

@@ -234,7 +234,7 @@ class GridFieldExportButton implements GridField_HTMLProvider, GridField_ActionP
                         }
 
                         $value = $columnHeader($relObj);
-                    } elseif ($gridFieldColumnsComponent && array_key_exists($columnSource, $columnsHandled)) {
+                    } elseif ($gridFieldColumnsComponent && in_array($columnSource, $columnsHandled)) {
                         $value = strip_tags(
                             $gridFieldColumnsComponent->getColumnContent($gridField, $item, $columnSource)
                         );